Liquid crystal display are rapidly developing in market, such as in clocks and watches, cellular phones, PDAs, notebook-sized personal computers, and monitor for personal computers, DVD players, TVs, etc. In the liquid crystal display, visualization is realized based on a variation of polarization state by switching of a liquid crystal, where polarizers are used based on a display principle thereof. Particularly, usage for TV etc. increasingly requires display with high luminance and high contrast, polarizers having higher brightness (high transmittance) and higher contrast (high polarization degree) are being developed and introduced. Very high reliability in heat resistance is especially required by a liquid display that is assumed to be used in a severe environment outdoors, such as cellular phones or PDAS, and a liquid display for vehicle navigation, a liquid crystal projector or the like.
As a polarizer, there has been widely used, for example, an iodine containing polarizer having a structure obtained by causing iodine to be adsorbed to polyvinyl alcohol and stretching the polyvinyl alcohol because of having a high transmittance and a high polarization degree. In the iodine -based polarizer, an iodine compound formed in a stretch step and working as a dichroic material is low in thermal stability. The iodine compound is modified very much and a dichroic performance is lowered in a test in which the compound is left in an atmosphere at 100° C. for a long time which simulates an environment on a dash board in an automobile in the middle of summer, which has resulted in a problem of a great decrease in function as a polarizer. Therefore, a dye-based polarizer using a dichroic dye instead of the iodine compound has been prevailed in a field having a strong requirement for reliability in heat resistance such as an application on a vehicle (see, for example, JP-A No. 62-123405).
The dichroic dye is; however, lower in absorption dichroic ratio than the iodine compound. Therefore, the dye-based polarizer is a little inferior in characteristic to the iodine-based polarizer. Adsorption of the dye easily causes unevenness in color dyeing and a state of uneven dispersion. Especially, when a black display is performed in a liquid crystal display, a mottled black display are presented, which has led to a problem of a great reduction in visibility.
In order to cope with this problem, a proposal has been made of a dye-based polarizer in which a quantity of adsorption or addition of dye is increased to lower a transmittance in black display to a perception limit or less with a human naked eye. The dye-based polarizer, however, lowers a transmittance in white display at the same time as a transmittance in black display, which causes a display itself to be darkened. Another proposal has been made of a production method for a dye-based polarizer in which a stretch process hard to generate unevenness is adopted (see, for example, JP-A No. 8-190015). The method, however, requires replacing a process proper, resulting in a reduced productivity.